security/keys/dh.c

   1 /* Crypto operations using stored keys
   2  *
   3  * Copyright (c) 2016, Intel Corporation
   4  *
   5  * This program is free software; you can redistribute it and/or
   6  * modify it under the terms of the GNU General Public License
   7  * as published by the Free Software Foundation; either version
   8  * 2 of the License, or (at your option) any later version.
   9  */
  10
  11 #include <linux/mpi.h>
  12 #include <linux/slab.h>
  13 #include <linux/uaccess.h>
  14 #include <keys/user-type.h>
  15 #include "internal.h"
  16
  17 /*
  18  * Public key or shared secret generation function [RFC2631 sec 2.1.1]
  19  *
  20  * ya = g^xa mod p;
  21  * or
  22  * ZZ = yb^xa mod p;
  23  *
  24  * where xa is the local private key, ya is the local public key, g is
  25  * the generator, p is the prime, yb is the remote public key, and ZZ
  26  * is the shared secret.
  27  *
  28  * Both are the same calculation, so g or yb are the "base" and ya or
  29  * ZZ are the "result".
  30  */
  31 static int do_dh(MPI result, MPI base, MPI xa, MPI p)
  32 {
  33         return mpi_powm(result, base, xa, p);
  34 }
  35
  36 static ssize_t mpi_from_key(key_serial_t keyid, size_t maxlen, MPI *mpi)
  37 {
  38         struct key *key;
  39         key_ref_t key_ref;
  40         long status;
  41         ssize_t ret;
  42
  43         key_ref = lookup_user_key(keyid, 0, KEY_NEED_READ);
  44         if (IS_ERR(key_ref)) {
  45                 ret = -ENOKEY;
  46                 goto error;
  47         }
  48
  49         key = key_ref_to_ptr(key_ref);
  50
  51         ret = -EOPNOTSUPP;
  52         if (key->type == &key_type_user) {
  53                 down_read(&key->sem);
  54                 status = key_validate(key);
  55                 if (status == 0) {
  56                         const struct user_key_payload *payload;
  57
  58                         payload = user_key_payload_locked(key);
  59
  60                         if (maxlen == 0) {
  61                                 *mpi = NULL;
  62                                 ret = payload->datalen;
  63                         } else if (payload->datalen <= maxlen) {
  64                                 *mpi = mpi_read_raw_data(payload->data,
  65                                                          payload->datalen);
  66                                 if (*mpi)
  67                                         ret = payload->datalen;
  68                         } else {
  69                                 ret = -EINVAL;
  70                         }
  71                 }
  72                 up_read(&key->sem);
  73         }
  74
  75         key_put(key);
  76 error:
  77         return ret;
  78 }
  79
  80 long keyctl_dh_compute(struct keyctl_dh_params __user *params,
  81                        char __user *buffer, size_t buflen,
  82                        void __user *reserved)
  83 {
  84         long ret;
  85         MPI base, private, prime, result;
  86         unsigned nbytes;
  87         struct keyctl_dh_params pcopy;
  88         uint8_t *kbuf;
  89         ssize_t keylen;
  90         size_t resultlen;
  91
  92         if (!params || (!buffer && buflen)) {
  93                 ret = -EINVAL;
  94                 goto out;
  95         }
  96         if (copy_from_user(&pcopy, params, sizeof(pcopy)) != 0) {
  97                 ret = -EFAULT;
  98                 goto out;
  99         }
 100
 101         if (reserved) {
 102                 ret = -EINVAL;
 103                 goto out;
 104         }
 105
 106         keylen = mpi_from_key(pcopy.prime, buflen, &prime);
 107         if (keylen < 0 || !prime) {
 108                 /* buflen == 0 may be used to query the required buffer size,
 109                  * which is the prime key length.
 110                  */
 111                 ret = keylen;
 112                 goto out;
 113         }
 114
 115         /* The result is never longer than the prime */
 116         resultlen = keylen;
 117
 118         keylen = mpi_from_key(pcopy.base, SIZE_MAX, &base);
 119         if (keylen < 0 || !base) {
 120                 ret = keylen;
 121                 goto error1;
 122         }
 123
 124         keylen = mpi_from_key(pcopy.private, SIZE_MAX, &private);
 125         if (keylen < 0 || !private) {
 126                 ret = keylen;
 127                 goto error2;
 128         }
 129
 130         result = mpi_alloc(0);
 131         if (!result) {
 132                 ret = -ENOMEM;
 133                 goto error3;
 134         }
 135
 136         kbuf = kmalloc(resultlen, GFP_KERNEL);
 137         if (!kbuf) {
 138                 ret = -ENOMEM;
 139                 goto error4;
 140         }
 141
 142         ret = do_dh(result, base, private, prime);
 143         if (ret)
 144                 goto error5;
 145
 146         ret = mpi_read_buffer(result, kbuf, resultlen, &nbytes, NULL);
 147         if (ret != 0)
 148                 goto error5;
 149
 150         ret = nbytes;
 151         if (copy_to_user(buffer, kbuf, nbytes) != 0)
 152                 ret = -EFAULT;
 153
 154 error5:
 155         kfree(kbuf);
 156 error4:
 157         mpi_free(result);
 158 error3:
 159         mpi_free(private);
 160 error2:
 161         mpi_free(base);
 162 error1:
 163         mpi_free(prime);
 164 out:
 165         return ret;
 166 }